Most motor vehicles are provided with radios capable of reception of frequency modulated (FM) signals in a commercial frequency or wavelength band known as an FM band. Such FM antennas must be mounted on the vehicle in such a manner that they are not electromagnetically shielded by the vehicle body structure from the signals they are intended to receive, which generally requires the antenna to be externally mounted or incorporated in a vehicle window. The traditional "whip" antenna is well known but is also often considered undesirable for various well know reasons, including the possibility of breakage due to accident or vandalism, an unsightly appearance, etc. This has led to attempts to incorporate the FM antenna into the vehicle body in a more protected and less visible way.
One place for mounting of a vehicle FM antenna is on the rear window of the vehicle, which is also often the location of an electric rear window defogger grid. The presence of the defogger grid on the window is helpful in that the antenna may be made of the same electrically conducting frit material as the defogger grid and applied to the inner surface of the rear window along with the defogger at minor additional cost. But the defogger grid is also a problem in taking up a majority of the window area and thus leaving a small area for the antenna. The result is a non-optimal FM antenna design which tends to have a reception band that is too narrow to encompass the complete commercial FM band and thus requires a separate boost amplifier located as closely as possible to the antenna. Such an amplifier adds significant additional cost, which it would be desirable to eliminate.
In addition, different countries have defined different FM bands for use within their borders; and an FM antenna for a vehicle is generally tuned to the FM band of the country in which the vehicle is intended for sale. But in the modern international economy, vehicle manufacturers wish to design and build vehicles for sale in different countries with common components and thus desire a broadband FM antenna capable of encompassing as many of the different commercial FM bands as possible.
Many rear window antennas or suggestions for such antennas exist which attempt to meet all these objectives, either with or without the inclusion of the rear window defogger grid into the antenna, but few have met all the objectives simultaneously.